People have been subject to lead exposure since the ancient times from various sources such as industrial emissions, children's toys, batteries, gasoline etc. In recent years, the Flint water crisis drew national attention to the dangers of lead pipelines. Since then, strict rules and regulations have fallen into place to reduce the levels of the toxic metal, which can create long-lasting health problems.

"Today, lead exposure is much lower because of regulations banning the use of lead in petrol, paints and other consumer products, so the number of deaths from lead exposure will be lower in younger generations. Still, lead represents a leading cause of disease and death, and it is important to continue our efforts to reduce environmental lead exposure," explained Professor Bruce Lanphear, from Simon Fraser University in Canada.

But even with the low levels of prevalence, the deadly impact of lead exposure may have been vastly underestimated. A study, led by Lanphear, suggested out of 2.3 million deaths every year in the United States, almost 412,000 deaths can be attributed to lead contamination. The figure is ten times higher than previous estimates reported by the Institute for Health Metrics and Evaluation.

"There's no safe threshold," Lanphear said. "Once we found that there was a risk across the entire range of exposures, we could estimate the number of attributable deaths. And instead of it being 40,000 deaths, which is what had previously been estimated, we found that it was about 10 times that."

Researchers also estimated 28.7 percent of cases of annual premature heart disease death in the country could be attributed to lead exposure, which comes to a total of 256,000 deaths per year.

Using data from the Third National Health and Nutrition Examination Survey, the study tracked 14,289 adults in the nation for two decades. Of the 4,422 who died by 2011, approximately 18 percent could have been saved by reducing blood lead concentrations to 1.0 micrograms per deciliter.

Compared to those with low lead levels, people with high lead levels (at least 6.7 micrograms) were at 37 percent greater risk of premature death from any cause, 70 percent greater risk of cardiovascular death, and double the risk of death from ischemic heart disease.

"Our study calls into question the assumption that specific toxicants, like lead, have ‘safe levels’, and suggests that low-level environmental lead exposure is a leading risk factor for premature death in the USA, particularly from cardiovascular disease," Professor Lanphear said.

Other experts have also expressed concern as another recent study suggested developing brains were harmed from exposure to air pollution even if it happens to be at the “safe level.”

"Estimating the contribution of low-level lead exposure is essential to understanding trends in cardiovascular disease mortality and developing comprehensive strategies to prevent cardiovascular disease. Currently, low levels of lead exposure are an important, but largely ignored risk factor for deaths from cardiovascular disease."

The researchers also strongly encouraged the retirement of lead-contaminated housing, lead-laden jet fuels, lead water pipes, and the reduction of emissions from smelters and lead battery facilities.